Utsuro no Hako to Zero no Maria Wiki
Kanji オー
Age Unknown
Gender Neutral
Status Alive
Classification Box Giver
Other Information

O, commonly misread as '0' (zero), is the antagonist of the series and the giver of 'Boxes' that 'grant wishes'. O has a strange curiosity with Kazuki Hoshino which is the source of much of the mayhem within the story.


O has no set appearance, instead, forming the image of everyone, yet resembling no one.[1] However, O has been known to take on the shape of both humans and other objects, such as Haruaki Usui after being 'rejected'[2], Kazuki Hoshino[3], Riko Asami[4] and the cinema guide 'A'[5]. It should be noted that 'A' is the only form of O that has been illustrated by Tetsuo, a.k.a 415, as shown below.

O as 'A'

Genderwise, O is neutral, being both male and female. Although this coincides with O not being able to distinguish between humans[6], the majority of the characters refer to O with 'he' or 'him'.[7]


'O' displays very different behavior from a normal human being. O is depicted with a large smile across his face. O goes to great lengths in order to be able to study Kazuki in several different environments.

Plot Wise[]

Spoiler warning!
This section contains plot details about the novels.

'O' has a large interest in Kazuki due to his way of thinking. After Kazuki denied the box that 'O' offered him, O began getting Kazuki involved in the situations of several other box owners in order to see how he would deal with them. 'O' often takes the form of another person close to Kazuki in each story in order study him up close rather than watching from outside the box.


  1. Kazuki Hoshino, Volume 1 Prologue: "It's just that he (she) somehow resembled everyone and no one at the same time."
  2. Volume 1, 27 756th time: His name is--
    And the moment I say his name—
    —Haruaki vanishes from his own face.
    It's not like his face changed shape. Haruaki just isn't present within the smile on his face anymore; it’s a fake who has disguised himself within Haruaki's skin.
  3. Volume 2 Prologue: When I say something like that to him, he laughs and changes his malleable appearance to that of someone familiar.
    Wearing my very own appearance, 'O' says...
  4. Volume 2, May 5th, Tuesday 23:00: Riko Asami opened her mouth in front of me.
    I raised an eyebrow. Something's wrong?
    "Huhu, I suppose you don't recognize me in this appearance. I am 'O'!"
  5. Volume 5, Daiya Oomine - 09/11 FRI 18:00:After hearing my explanation, the air around 'A' changes completely. Her smile is all too familiar.
    "Truly, I'm impressed."
    That smile is unmistakable.
    The person standing before me is 'O'.
  6. Volume 1 Prologue: I can’t distinguish one human from another human, even though I’m fascinated by humanity.
  7. A translation note in Volume 2 concerning Riko Asami addresses the fact that she was referred to as a 'he' because there is no English gender-neutral term, unlike in Japanese. It's plausible that this is also the reason 'he' is used mostly by the characters in reference to O, despite (presumably) Kazuki using "he (she)" when dreaming.